Friction engagement devices comprise friction plates and mating plates adapted to cooperate with each other.
Performance of friction engagement devices principally depends upon the performance of friction plates, especially, that of the friction materials. Conventional mating plates which are formed as simple one-piece plates are, in terms of the mechanical function, merely capable of receiving torque from the friction plates.
Conventional mating plates thus have drawbacks that the so-called "heat spots" are generated as result of the repetition of engagements and disengagements of the friction elements, or deformation due to the heat generated during use, which eventually causes the friction engagement devices to become unsuited for the intended use. Moreover, as result of use, coefficient of friction is likely to remarkably decrease, which requires that the so-called "safety factor" be set relatively high, which in turn requires the friction engagement device to be relatively large-sized as a whole.
In order to cope with these problems, it has been proposed that the mating plates be formed with grooves, or coatings having high heat conductivity. However, these measures merely intend to prolong the useful life of the mating plates on account of the cooling effect of those measures; and therefore, improvements of the fundamental performance of friction engagement devices are not obtainable, such as, the improvements in kinetic friction coefficient .mu..sub.D, static friction coefficient .mu..sub.S and the so-called .mu.-.nu. characteristics (namely, the ratio of kinetic friction coefficient, i.e., .mu..sub.D to friction coefficient when the relative rotation is zero, i.e., .mu..sub.0).
The object of the present invention is to provide mating plates capable of improving the abovementioned characteristics, suppressing change of coefficients of friction with the passage of time and preventing deformation due to heat.